A Winchester type magnetic disk drive has a hard magnetic disk with a diameter of 5.25 inches or 8 inches, several hundred circular recording tracks per inch and spacing of only several tens microns between adjacent tracks. In order to satisfactorily function, such a magnetic disk drive is required to accurately position the magnetic head, which writes and reads information to and from these record tracks, to the tracks within a predetermined error or tolerance, for example, a tolerance of several microns.
Even if positioning can be performed within the predetermined tolerance at a certain temperature, a temperature increase or decrease causes each component constituting the magnetic disk drive to expand or contract due to its linear expansion coefficient, which temperature change varies the relative positioning between the track and the magnetic head, so that the magnetic head can no longer be positioned within the allowable tolerance. If it is assumed that all the components constituting the magnetic disk drive have the same linear expansion coefficient, displacement of the magnetic head relative to the track can be prevented because all such components expand or contract in the same ratio, and do not vary the relative positioning between the track and the magnetic head. However, this does not occur in practice because components of material with various linear expansion coefficients are used.
Conventionally, the relative displacement between the magnetic head and track due to temperature change is compensated by incorporating a servo system in the magnetic disk drive. However, this increases the cost of the drive and therefore is difficult to employ in a relatively low cost magnetic disk drive.
Various low cost temperature compensating mechanisms for positioning magnetic heads have been proposed using mechanical elements. One of them is disclosed in the Japanese Laid-open Patent Specification No. 1695/80, in which a head actuator for positioning the magnetic head to a predetermined track on the magnetic disk comprises a step motor, two metal bands and a swivel arm, a pulley mounted on the shaft of said step motor housing and coil springs exerting tensile force on the metal bands, whereby temperature compensation is accomplished.